The present application relates to the field of radiation scanning and/or radiation imaging. It finds particular application with threat detection systems and/or explosive detection systems (EDS), such as those used to inspect baggage at security checkpoints. It also relates to other applications where it is desirable to inhibit the emission of radiation during an examination of an object or between an examination of a first object and an examination of a second object to perform a calibration procedure, comply with radiation emission regulations and/or conserve energy, for example.
Radiation systems, such as computed tomography (CT) systems, tomography systems, diffraction systems, projection systems, and/or line systems, for example, are used to provide information pertaining to interior aspects of an object. Generally, the object is exposed to radiation comprising photons (e.g., such as x-ray photons, gamma ray photons, etc.) to measure attenuation by the object or aspects of the object that interact with the radiation. Generally, highly dense aspects of an object absorb and/or attenuate more radiation than less dense aspects, and thus an aspect having a higher density, such as a bone or metal, for example, may be apparent when surrounded by less dense aspects, such as muscle or clothing.
In some applications, it is desirable to periodically or intermittently inhibit radiation from entering an examination region of the radiation system. For example, in some security applications, regulations may mandate that radiation systems inhibit radiation from being emitted into the examination region when no object is being examined (e.g., to limit radiation exposure during such instances). As another example, it may be desirable to limit exposure of a detector array to radiation during an offset calibration (e.g., also referred to as a dark calibration) when the system is measuring a response of the detector array when no radiation is being detected.
Several approaches have been used to inhibit radiation from entering an examination region and impinging upon a detector array. For example, according to one approach, a mechanical shutter is positioned proximate a focal spot (e.g., an opening) in a radiation source. When it is desirable to inhibit radiation from entering the examination region, an actuator adjusts one or more fins of the mechanical shutter, causing the fins to shield the focal spot and inhibit radiation from escaping the radiation source. Another approach has been to reduce an accelerating voltage applied to the radiation source (e.g., from an operating voltage of 180 kV to 0 V), effectively powering down the power supply, when it is desirable to inhibit radiation from entering the examination region. While such approaches have proven effective, both approaches have some disadvantages. For example, the mechanical fins are often slow to open/close and/or fail under rotation, and large swings in the voltage applied by the power source may be harmful to the power supply, radiation source, and/or other electrical components of the radiation system.